1. Field of the Invention
This invention relates to a process for discharging and transferring fluidized particles from a dense fluidizing layer forming section to a high-velocity transferring section having a diameter smaller than the dense fluidizing layer forming section.
2. Description of the Prior Art
Conventionally, fluidizing layers (beds) have been widely used in the treatments or chemical reactions of particles or gas. Fluidizing layers vary in form, and particularly fluidizing layers which circulate fluidized particles through the outer equipment have been applied to a reaction such as a petroleum catalytic cracking process which requires the continues regeneration of catalyst.
In order to improve the operation stability and reaction result of a system using such a circulating fluidizing layer, it is necessary to continuously circulate the fluidizing layer in a stable manner. For that purpose, it is important to permit the smooth continuous discharge, transfer and supply of particles from the fluidized layer. In recent years, there has been proposed a high-performance petroleum catalytic cracking process known as downflow type fluid catalytic cracking process hereinafter referred to as “downer type FCC”. In this process, the catalyst flows downwardly through the reactor. Therefore, thereafter it is necessary to transfer the catalyst upwardly while being regenerated. The present invention is the most effective when being applied to such a system.
Description of the Prior Art
Typical examples of conventional downer type FCC reactors are disclosed in Japanese Patent Publication Nos. 2,523,325 and 2,590,009. In these methods, the catalyst regenerator wherein a dense fluidizing layer is formed has an upper portion which is conical and connected to a high-velocity transferring section hereinafter referred to as “riser”, thereby making it possible to transfer the catalyst up to a height which is required by the downer, i.e., down flow reactor as well as continuous regeneration of the catalyst. In such systems, sufficient contact time required for the regeneration in the dense fluidizing layer can be ensured and the regenerated catalyst can be transferred and discharged by the riser without additional gas flow and mechanical operation.
However, although these systems excel in principle, they can not avoid the amount of particles to be transferred from the dense fluidized layer to the riser from varying due to the changes of the fluidizing state in terms of time and position which are peculiar thereto. As a result, there occur pressure loss in the riser and changes in the residence time of particles in the regenerator, leading to changes in the results of the treatments in the decomposition section and the catalyst- and adhered oil removing sections. These factors cause the decrease of the total reaction results and unstable operation.